Piezo-electric crystal reflecting mirror sound recording system



Aug.21,'1935. SQWHWMAN 1,012,797

PIEZO ELECTRIC CRYSTAL REFLECTING MIRROR SOUND RECORDING SYSTEM FiledJuly 15, 1954 2 Sheets-Sheet 1 IN V EN TOR.

. I I W WA TTORNEYS.

nmmx G BY Aug. 27, 1935. s. c. WHITMAN 2,012,797

PIEZO ELECTRIC CRYSTAL REFLECTING MIRROR SOUND RECORDING SYSTEM FiledJuly 13, 1934 2 Sheets-sheet 2 INVENTOR.

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I e I I I M W A TTORNEYS. J6

Patented Aug. 27, 1935 UNITED STATES v PATENT OFFICE PIEZO-ELECTRICCRYSTAL REFLECTING MIRROR SOUND RECORDING SYSTEM Stewart 0. Whitman,Sunnyside, Long Island, N. Y.

Application July 13, 1934, Serial No. 735,074 18 Claims. (01. ire-100.3)

A further object of my invention is to provide 7 10 a system for varyinga light beam at sound frequencies while avoiding the employment of theelectro-magnetic effect of a current actuating an armature element in amagnetic field.

A still further object of my invention is to pro- 15 vide apiezoelectric crystal actuated mirror element in which the metallaminated electrodes themselves constitute the mirror.

Heretofore in the art there has been employed a regular oscillographmirror and .element 20 through which current is passed to vary a lightbeam, this being' an electro-magnetically actuated arrangement. Themoving parts of such a system possess considerable inertia, and being acurrent operated device, consume considerable 25 power, which requiresconsiderable amplification, which in turn is likely to introducedistortion.

I provide a piezoelectric crystal or other electromechanical vibratileelement carrying a mirror at a point where such element vibrateswith'consi d- 30 erable amplitude under the action of an applied voltageof audio-frequency. A beam from a sou ce of light is incident upon suchmirror and is thereby reflected'through a suitable optical system uponthe sound track of a sensitive film.

My invention is directed primarily to a light sensitive motion picturefilm having a sound track.

With these and numerous other objects in view, my invention consists inthe novel features of construction, combination and arrangement of partsas will be hereinafter referred to and more particularly pointed out inthe specificationand claims.

In the accompanying drawings forming a partlof 45 this application:

' Figure 1 shows a general view of the assembled system for recordingsound on film, including the light reflecting piezoelectric crystalelement;

Figure 2 shows a sectional view of the cylin- 50 drical lens andrevolving slot unit herein employable of the type disclosed in mycopending application, Serial No. 605,992;

Figure 3 shows a front view of a wedge-shaped type of piezoelectriccrystal element mounted at 55 one end;

Figure 4 shows a side elevation of the element of Figure 3;

Figure. 5 shows a sectional view on the line 5-5 of Figure 3;

Figure 6 shows a horizontal section on the line 5 66ofFlgure3; Y

Figure 7 shows a pivotally mounted elliptical form of piezoelectriccrystal element;

Figure 8 shows a filarly mounted piezoelec tric crystal element in theform of an elongated v isosceles trapezoid;

Figure 9-shows a fllarly mounted circular form of piezoelectric crystalelement;

Figure 10 shows a front elevation of a modification of my inventionemploying two parallel l5 ofiset piezoelectric crystal elements with amirror element mounted between their ends in parallel relation;

Figure 11 shows a side elevation of the arrangement of Figure 10,looking in the direction of the arrow A of Figure 10;

Figure 12 is a general schematic view of the arrangement of Figure 10,including the wiring of the circuit; v,

Figure 13 shows a further modification of my invention, employing twooffset piezoelectric crystal elements and a ribbon provided with. a'mirror portion maintained in contact with their ends;

Figure 14 shows a'detailed view of the ribbon element and its mirrorportion of the arrangement of Figure 13; and

Figure 15 shows a modification of the arrangement of Fig. 13 wherein theribbon element is controlled by a pair of surrounding inductance coils.

I have found that a desirable form of piezoelectric crystal element isRochelle salt crystals protected with some material such as collodionagainst deliquescence. It .has also been found 1 that a crystal havingthe shape of an elongated wedge or isosceles trapezoid has desirablefrequency operating characteristics. In a preferred embodiment of myinvention, I employ electrodes for the piezoelectric crystal elementwhich consist of metallic laminae aflixed to the crystal which have highlight-reflecting ability, whereby there is avoided the additionalinertia of a separate found that a system employing crystals of the typehere described operates satisfactorily on all frequencies throughout theaudio range, wherein the system of my invention has a marked advan- Iinertia due to the weight of the glass mirror and its supports. Such aconventional oscillograph mirror is essentially a mechanical system, andrequires much more energy for its operation than the system of myinvention.

The system of my invention employing a piezoelectric crystal element isessentially a voltage operated device, whereas the conventionaloscillograph mirror system is essentially a current operated device, andalso for that reason requires more energy.

In employing a piezoelectric crystal element, there is available only acomparatively small amount of power, since it is a voltage operateddevice and it is desirable so far as possible to avoid attachingextraneous mobile elements to the crystal to be actuated by the crystal;for this reason, it is particularly desirable to use the arrangementwhich I disclose in which optical reflection takes place directly fromthe metallic reflecting surface of the laminar metallic electrodes whichare directly affixed to the crystal itself. The conventionaloscillograph mirror type of system heretofore employed has sharpfrequency characteristics which limit its usefulness to a comparativelynarrow part of the audio-frequency spectrum. When a piezoelectriccrystal element is vibrating under the action of an applied voltage, itwill often be found that the addition of even a very light mirrorelement .or other slight weight to the crystal will entirely stopvibrations. The crystals, which I employ are-cut and ground in theshapes which ,I describe to cover the desired audio-frequency range fromthe lowest tothe highest audio-frequency. A convenient form of electrodewhich I have employed consists of tin foil, wherein the portion of theelectrode upon which thelight bearnffalls is well polished to constitutea good optical reflecting surface. The area of the electrode upon whichthe light beam is incident should be so located.

as to be at a point of relatively large displacement of the crystalelement during vibration.

In order to increase the relatively small amount of power available froma single crystal element, it is usual to employ a stack of crystalsarranged as layers constituting a laminated crystal unit, with theelectrodes interleaved. In my invention, the foil constituting the outerelectrode is teenth of an inch, and through the cylindrical lens l0 uponthe sound track I I of the motion picture film l2.

Instead of the simple cylindrical lens element ill of Figure 1, theremay be advantageously employed a specialized form of cylindricallenswith a special revolving slot l3 (Fig. 2) as fully shown and describedin my copending application Serial No. 605,992, filed April 18th, 1932,which form has particular advantages for the purposes here in view. a 1

Figure 3 shows an elongated wedge-shaped form of crystal 5 mounted atone end flxedly on the base 841 which mayadvantageously be of somematerial such as bakelite. It is desirable to make the free end of thisform of crystal element of a rounded shape as shown. The binding posts 6and I mounted on the base 8a are connected to the. electrodes in theform of thin metal laminae which occupy substantially the entire area ofthe crystal faces. Since the free end of this form of crystal willordinarily be the point of maximum displacement during the vibration, itis desirable to have the electrodes polished adjacent this rounded freeend so that the light beam may im pinge thereon for reflection.

By making the crystal wedge-shaped, tapered towards the top, an enhanceddisplacement effect is obtained, since the cross-sectional resistanceand piezoelectric response of the crystal increases as the widthdecreases with increasing height above the base, and a differentialeffect is produced.

As shown in Figures 4, 5 and 6, the piezoelectric crystal element 5 isprovided with the laminar electrodes 4 and 4a. which are substantiallyof equal area and symmetrically disposed on the crystal element.

In Figure 7, there is shown an elliptical form of piezoelectric crystalelement having the electrode l0 occupying substantially the entire areaof the crystalface. This electrode is also formed of a metallic laminaand is polished in the area of maximum displacement during vibration tohavegood light reflecting properties. The-crystal element 9 is supportedby the frusto-conical means II and I2 which are attached to the frameii. The means II and I2 may be adjusted by the screw means I! and I5.One of the means, as l2, engages the crystal 9 tightly so .as to hold itrigidly, or at least much more tightly than the other means as H. Thecrystal is mounted to move substantially freely pivotally on one of themeans, as H. p

In Figure 8, the piezoelectric crystal element I6 is in the form of anisosceles trapezoid having its long dimension in the direction of itsnon-parallel edges. The electrode l1 occupies substantially the entirearea of the crystal face. The

surface of the electrodes I1 is also well polished in the area of itsmaximum displacement during vibration. Wire elements l8 and I! areflxedly attached to the parallel edges of the crystal at approximatelythe central point thereof so that the crystal is mounted on its axis oflongitudinal symmetry. These wires are tightly attached to the mountingterminal members 20 and 2| which may be adjusted by the screw adjustingmeans 22 and 23, respectively. These screw adjusting means are in turncarried on the frame 24. One 'of these wires as I9 is relativelyinflexible and stiff, as hard-drawn steel or phosphor-bronze wire, or astiff ribbon wire. The other wire as N is relatively quite flexible andsoft-drawn, to permit free movement of the upper end of the crystalrelative to terminal member 20. This form of crystal element has beenfound to have decided advantages in its operating characteristics,particularly as to frequency range. The connections ,to the electrodesmay advantageously be made directly through the wires i8 and I9.

In Figure 9, the piezoelectriccrystal element 25 is of substantiallycircular form, and is provided with the electrodes 26 which occupysubstantially the entire area of the crystal face. This electrode isalso preferably a thin metallic lamina One of these wires as 28 islikewise relatively inflexible and stifi, as hard-drawn steel orphosphor-bronze wire, or a stifi ribbon wire. The other wire, as 21, isrelatively quite flexible and soft-drawn, to permit free motion of theupper end of the crystal relative to terminal member 29.

The means employed for mounting the crystals in the arrangements shownin Figs. 7, 8, and 9, including the one relatively stiff mounting whichis adjustable, provides means for controlling he damping effect and thefrequency response of the crystal, so that small adjustments forfrequency can be made. By selecting wire of suitable diameter andelasticity, and properly adjusting the tension by the adjus ing screws.the frequency response characteristics of the wire can be varied.

Figure 10 shows a modified form of my invention employing two piezoelectric crystal elements 34 and 35 which are mounted in substantiallyparallel relation on the base 36 which may advantageously be ofbakelite. The crystal 34 is provided with electrodes 36 and 31, and thecrystal 35 is provided with the electrodes 38 and 39. These electrodesoccupy substantially the entire area of the crystal faces. The crystal35 is s:mewhat shorter than the crystal. 34, so that the crystals havean offset relationship. The crystal 34 has a terminal arm orbridgemember 40 attached at its free end, and the crystal element 35 has thearm or bridge member 4| attached at its free end. These arms extendtoward each other as shown, and should preferably be of as light weightand structure as will serve the purpose, in order to reduce to a minimumthe inertia of the moving parts. These arms are called uprn to standcompressive stresses wihout bending, but since these stresses are ofcomparatively small magnitude, the arms may be constituted of sturdynon-bending wire such as phosphor-bronze wire. Between the free ends ofthe arms 40 and 4|. the mirror element 42 is disposed, and is held inplace by the arms 40 and 4|. The mirror element 42 should be of as smallarea and of as light weight and structure as will serve the purposes.This mirror should have high optical reflecting power. As shown, mirrorelement 42 is advantageously mounted substantially parallel to the longdimension of crystal 34 and with an air space between mirror element 42and crys al 34, so that mirror element 42 is in heat-insulated relationto crystal 34, which arrangement has particular advantages when a veryintense beam of light is to be used with a crystal adversely aifected byheat. Under the action of the voltage applied between its electrodes,crystal 34 bends or flexes or buckles and thereby laterally displacesits free end. Likewise, under the applied voltage, crystal 35 bends andlaterally displaces its free end. The crystals 34 and 35 are so selectedand so connected that under the ac. ion of an applied voltage thecrystal 35 is displacing its free end toward the left when the crystal34 is displacing its free end toward the right, as shown by-the arrowsin Figure 10. Due to this fact, when a voltage is applied, the mirror 42is tilted through an angle whose amplitude depends upon the appliedvolt- I'hese screw means are carried on the age. The arrangement of themirror 42 may be clearly seen in Figure 11; Figure 12 shows a generalschematic view of this arrangement and also the connections 43, 44, 45and 46 to the electrodes of the crystal. The transformer 41 has aprimary 49 and a secondary 48. The applied audio signal is connected tothe'primary 49. The secondary48 is provided with a mid-tap 53 to whichthe electrode connections 44 and 45 are connected. The terminals ofsecondary 48 are connected to the other electrodes of the crystal by the'wires 43 and 46. This constitutes a push-pull arrangement by which. thecrystals act in opposition as previously described, and the mirrorelement 42 is tilted under the action of the applied voltage of thesignal.

' It is desirable to have a relatively large value of impedance forcoupling the crystal to the input circuit, for either recording orreproducing, in order to match the relatively large impedance of thecrystal itself, the crystal being inherently a small-current andsmall-power device.

- Figure 13 shows a further modification of my invention employing twopiezoelectric crystal elements and 52 which are mounted in offsetrelaticnsh'p. The crystal element 5| has the electrodes 53 and 54, andthe crystal element 52 has the electrodes 55 and 56. These electrodesoccupy substantially the entire area of the crystal faces. Thesecrystals are preferably mounted on a frame 57 by one end of eachcrystal, in such manner that the free ends of crystals 5| and 52 are insubstantially the same vertical plane, the crystals being mounted fromopposite directions with reference to such plane. Under the action ofthe voltage applied to its electrodes, each of the crystals 5| and 52bends or flexes or buckles and thereby foreshortens and lengthens, anddisplaces its free end. A ribbon element 58 is held tautly aga'nst thefree ends of crystals 5| and 52. This ribbon element 58 is preferably anarrow metallic band or ribbon and passes over pulley or similarsupporting means 59 and 60, and is held securely in place by adjustabletension means 6| and 62. A, a point intermediate crystals 5| and is usedfor light reflection should be silvered or otherwise provided with avery gocd optical reflecting "surface. Figure 14 shows a detail of theribbon 58 and the reflecting portion 53. The electrodes of the crystalelement are respectively connected to binding posts 54, 55, and 61, towhich the audio frequency voltage is applied in proper relationship sothat crystals 5| and 52 will operate in push-pull relationship, in amanner similar to that shown in Figure 12.

While in Fig. 13, I have shown two crystals mounted offset in opposedrelation, it is also possible to use in the arrangement of Fig. 13 onlyone crystal as 52, and to substitute a rigid fret for the other crystalas 5|, and the system will operate but with decreased amplitude.

.Figure 15 shows an additional means for securng good control of themodification shown in Figure 13. In Figure 15, the crystals 5| and 52,and the ribbon element 55 with its reflecting portion 63, aresubstantially as shown in Figure 13.- There are, however, provided inaddition, the

solenoids or inductance coils 68 and 69 which surround the metallicribbon element 58. The solenoid 68 is wound in the opposite sense tosolenoid 69. The terminals 10 and H of solenoid 68, and the terminals 12and 13 of solenoid 69, are connected to sources 14 and 15 of directcurrent which are so poled that solenoid 69 has a field of senseopposite to that of solenoid 68. These solenoids therefore applymagnetic fields of constant magnitude in opposite sense to the metallicribbon 58 which materially assist in controlling the ribbon and holdingit in place, and avoiding undesired free vibrations of the ribbon. Thismaterially assists in maintaining the accuracy of the sound trackobtained.

I have found that the type of piezoelectric crystal element reflectingsystem which I have described has important desirable operatingcharacteristics which are not possessed by the types of devicesheretofore known in the art, and that very sharp and accuratelydelineated sound recordsmay be thereby attained.

From the foregoing description of the construction of my improvedrecording system, the operation thereof and the method of applying thesame to use will be readily understood. It will be seen that I haveprovided a simple, inexpensive and efficient means for carrying out theobjects of the invention and while I have particularly described theelements'best adapted to perform the functions set forth, it is obviousthat various changes in form, proportion and in the minordetails ofconstruction may be resorted to, without departing from the spirit orsacrificing any of the principles of the invention.

Having thus described the invention, what is claimed is:

1. In a system for recording sound on film, a source of light, avibratably mounted piezoelectric crystal, electrodes for said crystal, alaminar mirror element mounted on said crystal flatly on a face oflargest area thereof and at a point ofrelatively large displacement ofsaid crystal and displaceable by the vibrations'of said crystal, alight-sensitive film having a sound track and positioned so that lightfrom said source incidentv on said mirror element is reflected on saidsound track, and a source of electric energy of sound frequencyconnected to said electrodes.

2. In a system for recording sound on film, a source of light, avibratably mounted piezoelectric crystal element, laminar metalliclight-reflecting electrodes affixed to said element, said element beingpositioned so that light from said source is incident upon one of saidlight-reflecting electrodes, a light-sensitive film having a sound trackand positioned so that-light from said source incident on said electrodeis reflected on said sound track, and a source of electric energy ofsound frequency connected to said electrodes.

3. In a system for recording sound on film, a source of light, avibratably mounted long wedgeshaped piezoelectric crystal element,laminar inetallic light-reflecting electrodes ,afllxed to said element,said element being positioned so that light from said source is incidentupon one of said light-reflecting electrodes, a light-sensitive filmhaving a sound track and .positioned so that light from said sourceincident on said elec-,- trode is reflected on said sound track, and asource of electric energy of sound frequency connected to saidelectrodes.

4. In a system for recording sound on film, a source of light, avibratably mounted piezoelectric crystal element, said element havingsubstantially the shape of an isosceles trapezoid with its longestdimension in the direction of its non-parallel edges, laminar metalliclight-reflecting electrodes afiixed to said element, said element beingpositioned so that light from said source is incident upon one of saidlight-reflecting electrodes, av light-sensitive film having a soundtrack and positioned so that-light from said-source incident on saidelectrode is reflected on said sound track, and a source of electricenergy of sound frequency connected to said electrodes.

5. A unit for varying a light beam in accordance with impressedelectrical variations comprising a vibratably mounted piezoelectriccrystal element, and laminar metallic light-reflecting electrodesaflixed to said element and having an optically good reflecting surfaceat a point of relatively large displacement of said crystal elementduring vibration.

6. A unit for varying a light beam in accordance with impressedelectrical variations comprising a vibratably mounted long wedge-shapedpiezoelectric crystal element, and laminar metallic light-reflectingelectrodes afiixed to said element and having an optically goodreflecting surface at a point of relatively large displacement of saidcrystal element during vibration.

7. A unit for varying a light beam in accordance with impressedelectrical variations comprising a long substantially wedge-shapedpiezoelectric crystal element, means for fixedly mounting said elementon the broader end thereof, said element being freely movable at thewedge-point end thereof, and laminar metallic light-reflectingelectrodes afiixed to said element and having an optically goodreflecting surface at a point of relatively large displacement of saidcrystal element during vibration.

8. A unit for varying a light beam in accordance with impressedelectrical vibrations comprising a substantially ellipticalpiezoelectric crystal element, means for mounting said element atdiametrically opposite points thereof, said crystal beingrelatively'fixedly mounted at one of said points and substantiallyfreely pivotally mounted at the other of said points, and laminarmetallic light-reflecting electrodes afiixed to said element and havingan optically good reflecting surface at a point of relatively largedisplacement of said crystal element during vibration.

9. A unit for varying a light beam in accordance with impressedelectrical vibrations comprising a piezoelectric crystal element havingsubstantially the shape of an isosceles trapezoid with its longestdimension in the direction of its non-parallel edges, means for mountingsaid element on the parallel edges thereof, on its axis of longitudinalsymmetry, said crystal being relatively fixedly mounted on one of itssaid parallel edges and substantially freely swingably mounted on theother of its said parallel edges, and 5 ance with impressed electricalvibrations comprising a piezoelectric crystal element havingsubstantially the shape of an isosceles trapezoidwith its longestdimension in the direction of its non-parallel edges, a pair of filarsupporting elements fixedly attached respectively to the par;-

' 15. A unit for varying a light beam in acallel edges of said elementat the central points thereof, one of said filar elements beingrelatively inflexible and the other of said filar elements beingrelatively highly flexible, supporting means to which said filarelements are fixedly attached, and laminar metallic lightreflectingelectrodes aflixed to said element and having an optically goodreflecting surface at a point of relatively large displacement of saidcrystal element during vibration.

11. A unit for varying a light beam in accordance with impressedelectrical vibrations comprising a substantially circular piezoelectriccrystal element, a pair of filar supporting elements fixedly attachedrespectively at diametrically opposite points ofsaid element, one ofsaid filar elements being relatively inflexible and the other of saidfilar elements being relatively highly flexible, supporting means towhich said filar elements are fixedly attached, and laminar metalliclight-reflecting electrodes aflixed to .said element and having anoptically good reflecting surface at a point of relatively largedisplacement of said crystal element during vibration.

12. A unit for varying a light beam in accordance with impressedelectrical vibrations, comprising a pair of piezoelectric crystalelements, electrodes for each of said elements, means for fixedlymounting one end of each of said elements and maintaining said elementsin substantially parallel relationship and adjacent each other, one ofsaid elements having its end opposite its mounting end projecting beyondthe free end of the other of said elements, a laminar mirror element,and a pair of arms attached to separated points of said mirror elementand respectively to the free ends of said crystal elements formaintaining said mirror element in a position approximately parallel tosaid crystal elements.

13. In a system for recording sound on film, a source of light, a pairof piezoelectric crystal elements, electrodes for each of said elements,

means for fixedly mounting one end of each of said elements andmaintaining said elements in substantially parallel relationship andadjacent each other, one of said elements having its end opposite itsmounting end projecting beyond the free end of the other of saidelements, a laminar mirror element; a pair of arms attached to separatedpoints of said mirror element and respectively to the free ends of saidcrystal elements, alight-sensitive film having a sound track andpositioned so that light from said source incident on said 'mirrorelement is reflectedon said sound track, and a source of electric energyof sound frequency connected to said electrodes.

14. A it for varying a light beam in accordance with impressedelectrical vibrations, comprising a pair of piezoelectric crystalelements, electrodes for each of said elements, a mounting frame whereonone end of each of said crystals is fixedly mounted in such manner thatsaid crystals occupy substantially parallel offset planes, the ends ofsaid crystal elements opposite said mounting ends being free, a ribbonelement in contact with the free ends of said crystal elements, andmeans for maintaining said ribbon element taut and in close contact withthe ends of said crystal elements, said ribbon element beingprovidedintermediate said crystal elements with an integrallyformedoptically reflecting mirror portion.

cordance with impressed electrical vibrations, comprising a pair ofpiezoelectric crystal elements, electrodes for each of said elements, amounting frame whereon one end of each of said crystals is fixedlymounted in such manner that said crystals occupy substantially paralleloffset planes, the ends of said crystal elements opposite said mountingends being free, a metallic ribbon element in contact with the free endsof said crystal elements, means for maintaining said ribbon element tautand in close contact with the ends of said crystal elements, said ribbonelement being provided intermediate said crystal elements with anintegrally formed optically re fleeting mirror portion, a pair ofsolenoids surrounding said ribbon element and positioned on oppositesides of said mirror portion, and sources of direct current connectedrespectively to said solenoids, said solenoids being so wound andconnected as to apply to said ribbon magnetic fields of opposite sense.

16. A unit for varying a light-beam in accordance with impressedelectrical vibrations, comprising a piezoelectric crystal elem'ent,electrodes for said crystal element, a mounting frame' whereon one endof said crystal element is fixedly mounted and carrying said crystalelement with its other end free, fret means carried by said mountingframe and extending from said mounting ,frame substantially parallel tosaid crystal element, said fret means being positioned in a plane offsetfrom the plane of said crystal element, a ribbon element in contact withthe free end of said crystal element and the free end of said offsetfret means, and means for maintaining said ribbon element taut and inclose contact with the end of said crystal element and the end of saidfret means, said ribbon element being provided intermediate said crystalelement and said fret means with an integrally formed opticallyreflecting mirror portion.

17. In a system for recording sound on film, a source of light, avibratably mounted piezoelectric crystal, electrodes for said crystal, amir ror element attached to and carried by said crys-. tal in spacedrelation thereto at a point of relatively large displacement thereof anddisplace-' able by vibrations of said crystal, said mirror element beingmounted substantially parallel to the long dimension of said crystal andforming with said crystal an intervening air space, a lightsensitivefilm having a sound track and positioned so that light from said sourceincident on said mirror element is reflected on said sound track, and asource of electric energy of sound frequency connected to saidelectrodes. 18. In a system for recording sound on film, a

S'IIIEWART c. WHITMAN.

